Studies on the mechanism of the occurrence of hollow root in 'Gensuke'

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Gensuke daikon has been cultured in the sand dune regions of Ishikawa Prefecture because of its high quality. When the radish is sown in midsummer, "hollow root" which has lengthwise hollow in the central part of the root has been frequently observed. This research was carried out to elucidate the mechanism of the occurrence of hollowness in the root.When Gensuke was cultivated under high temperature or treated with high concentration of auxin from sowing to 30 days after sowing, root growth during that period was severely suppressed with high occurrence of hollow root. The occurrence of hollow root was high when the rate of weight growth by divided the root weight on the 60th day after sowing by that oh 30th day was large, but the occurrence was low when the rate was small. In this cash, vessels in the root bifurcated rapidly in the former, but the space among vessels was small in the latter. This result shows that root growth is accelerated by the active proliferation of parenchymatous cells in the former, but the growth is suppressed by the poor proliferation of the cells in the latter.The lysigenous intercellular space developed to the hollow with rapid root growth. The space would not develop to the hollow under the suitable condition because the space continued to be filled up with parenchymatous cells, but the space developed to the hollow under the unsuitable condition because the space could not be filled up with the cells owing to the poor proliferation of the cells.In cultivars resistant to hollowness the proliferation of parenchymatous cells was not suppressed even under high temperature, hollow root did not occur as the lysigenous intercellular space continued to be filled up with the cells.Summing up these results, whether or not the lysigenous intercellular space develops to hollow is decided by the balance between the degree of development of the lysigenous intercellular space and the degree of the filling of the space by parenchymatous cells.